1. Field of the Invention
The present invention relates to a vent cap for a storage battery, and in particular, it relates to a vent cap for a storage battery (or referred to as a storage-battery vent cap), which adjusts an internal pressure of the storage battery by exhausting a gas generated inside the storage battery to the outside and blocking inflow of external air.
2. Description of the Related Art
A lead storage battery is a rechargeable battery which can be repeatedly charged and discharged by an oxidation-reduction reaction generated between sulfuric acid serving as electrolyte and two plates formed of lead and lead oxide. The lead storage battery typically includes a plurality of plates (positive plates and negative plates) which are alternatively arranged and separators for separating the adjacent plates, and sulfuric acid serving as electrolyte solution is filled in spaces other than the plates and the separators.
The lead storage battery has high reliability and stability satisfying many characteristics required as the rechargeable battery since it has developed for a long period of time. Further, the lead storage battery shows systematized high technical completeness and has been applied to various fields at a low cost.
However, since water of the electrolyte solution is decomposed deteriorating performance of the battery, the lead storage battery needs periodic water supplement, which is a troublesome job. As one of the methods for solving such a problem, a study on a technique for sealing the lead storage battery has been developed.
A valve regulated lead acid (VRLA) storage battery is one of such sealing-type lead storage batteries. The VRLA storage battery has design differences in applications of a special separator, called as an absorbent glass mat (AGM) having an absorption function of the electrolyte solution, high-compression of plates, and low resistance. The VRLA storage battery also has an operational difference in that hydrogen gas and oxygen gas generated by the water decomposition of the electrolyte solution when overcharged are reduced and returned to the inside thereof through a gas-recombination operation.
As in the VRLA storage battery, when a sealed lead storage battery is overcharged, electrolyte solution is electrolyzed so as to generate hydrogen gas and oxygen gas, thereby increasing an internal pressure of the battery. This increase of pressure caused by the generated gases not only deteriorates performance of the battery but also involves the risk of exploding a case of the battery. Accordingly, means for exhausting a gas generated inside the storage battery to the outside and blocking inflow of external air should be developed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.